Next-generation military communications challenges
Military communications (MILCOM) has been the backbone for deployed soldiers since the Vietnam War. While these units have proven their capability and security for decades, the next generation of MILCOM platforms will need to leverage more modern communication technologies that have been developed to enable commercial platforms such as cellphones and Wi-Fi.
Systems used for military communications (MILCOM) are often handheld units – walkie-talkies – with a push-to-talk (PTT) button that the users can press when they need to relay a voice message. When the PTT button is not depressed, an incoming voice message can be received from another walkie-talkie. The voice message relayed between two radios is modulated, encrypted, amplified, and transmitted wirelessly between the two soldiers. Many differences exist between these MILCOM walkie-talkies and a commercial cellphone or communication system, just a few of which are shown in Table 1.
Next-generation MILCOM platforms face the challenge of maintaining several of these critical differences, while closing some of the gaps between military and commercial communications systems. These MILCOM platforms will need to change from voice-only systems by adding data and text capability. This shift will enable the delivery of data such as mapping, images, and video to a soldier in the battlefield. The issue is that wider bandwidths create challenges for the radio platforms, primarily around size, weight, and power (SWaP).
The traditional radio frequency (RF) signal chains used by MILCOM platforms will not scale to wider bandwidths and digital modulation schemes without consuming much more power, and they will also increase in size and weight. This growth in SWaP is unacceptable to the soldier, who needs a smaller, more capable radio that can be powered for long mission durations on minimal battery power. Thus, next-generation MILCOM platforms will require new RF signal chain architectures.
Shrinking the radio design
One revolution in small-form-factor radio design has been integrated RF transceivers. Integrated transceivers reduce size and power by repartitioning the radio in several ways. First, RF and analog devices can be transferred to the digital domain – RF filters becoming digital filters, for instance. The digital implementations of these blocks are more efficient and more programmable than their RF counterparts.
Second, discrete RF signal chains are often heterodyne architectures, which require several layers of frequency conversion, filtering, amplification, and digital sampling. Integrated transceivers can use a zero-intermediate frequency (ZIF) architecture that drastically reduces the required components in the signal chain, specifically the required filtering and amplification stages. Removing these stages reduces both size and power draw.
Finally, the ZIF architecture is a more efficient use of the digital converters, which in a wideband system can drive overall power consumption. While commercial platforms have been able to take advantage of ZIF transceivers for the last decade, the first products with MILCOM-applicable features have only come to market in the last few years.
What’s needed for the backbone of the MILCOM radio circuitry is integrated transceivers, which are making great strides toward providing single-chip solutions that will integrate the bulk of the receiver and transmitter signal chains while maintaining features such as frequency-hopping, AGC, and the ability to upgrade to future waveforms. Building on these transceivers as a core block of the radio will enable the next generation of MILCOM radio systems.
The ADRV9009 (Figure 1) is a CMOS transceiver with several MILCOM-appropriate features. First, the device is a native time duplex device (TDD), which is how a PTT architecture typically operates; this setup saves power compared to having two local oscillators (LO) in the device. The integrated LO supports frequency-hopping natively in the transceiver, both from a frequency-generation perspective and a calibration perspective.
The usable bandwidth can be programmed between 20 MHz and 200 MHz, enabling a range of wide bandwidth operating modes. It’s also waveform-agnostic, which means that it delivers RF to bits with no limits on what waveform is used; this will allow for implementation of waveforms that are available both now and those introduced in the future. Finally, the ADRV9009 integrates several auxiliary features into the transceiver. Automatic gain control (AGC) is critical for optimizing the receiver dynamic range, and the ADRV9009 has an internal AGC loop with 30 dB of range. Temperature sensors, control converters, and general-purpose outputs (GPOs) are also integrated into the device to save space in the MILCOM radio system.
Analog Devices, Inc. www.analog.com